Craig White's Literature Courses Terms / Themes classic, popular, and representative literature These categories are  not mutually exclusive.

A classic gets popularized!

Classic literature or art is above all works that survive through institutions like schools, religious traditions, or learned societies. Classical literature enjoys a long shelf-life but its popularity may be limited to literate, elite, or schooled culture. Compared to popular literature, classic literature is under-exposed except in schools.

"A classic is something everybody wants to have read, but no one wants to read."—Mark Twain

Twain's line is funny for sympathizing with humanity's weaknesses, but "wants to have read" admits the prestige or social capital of classics.

In Literature's ongoing balancing act between entertainment and education, classic literature tilts toward education or learning and is less likely to indulge cheap thrills or escapism.

"Education" may include broadening the mind, cultural literacy, vocabulary-building, modeling, ethics, empathy, critical thinking, cultural or historical critiques concerning social or personal justice, mental-emotional exercise,  attention-span extension (deferred gratification), and discipline.

Popular literature and culture are what most people want to read, largely because they're easier and more immediately gratifying. They stick to proven formulas (as in "sequels" or "knock-offs") to capitalize on previously-proven winners. They're familiar and unchallenging, in contrast to the demands classic literature makes on a reader.

A classic text, instead of being highly predictable, self-consciously innovates, extends, reforms, or even parodies previous styles and contents from earlier texts in its tradition. Like evolution, classic literature continues what has come before but also adapts to fresh experience and challenging knowledge. (Popular literature also changes but follows rather than leads, supporting status quo.)

A simple formula for classic literature is "a book that won't stay closed." A classic text keeps producing meaning for one generation after another, in different contexts, for audiences with different mind-sets and needs—even though the text still speaks with the same words! 

Classics don't always stay classics, though. Competition from new texts is always crowding out some older ones, and tastes and needs change.

In sum, what counts as "classic literature" remains fairly stable but also changes according to what's being written, what gets taught, and who's sitting in the classrooms. (See representative literature below.)

Popular literature or art is the kind of literature that readers talk about excitedly and want to read as though it is news or a change in lives of people they care about—for instance, a new installment in a series like Twilight, Hunger Games, Tom Clancy's novels featuring Jack Ryan, or any other detective, spy, or action series with a glamorous, super-competent hero or team.

Instead of surviving indefinitely in schools and libraries, popular literature lives and dies by the momentary marketplace when it appears in popular culture. Successful popular literature sells well and becomes well-known to a wide audience, but compared to classic literature or art it is often over-exposed, shorter-lived, and soon forgotten or replaced with follow-ups, sequels, etc. (e.g., hit songs on the radio sound old a month or year later).

Sentimental style, sensational events, and stereotypical formulas like sensitive vampires, exploding helicopters, helpful dogs, and lost children are predictable, but they please wide audiences by reinforcing familiar tastes and attitudes, confirming what everybody already thinks and appealing to what is already known.

(In contrast, classic literature usually takes you beyond your comfort zone.)

Representative literature / art (sometimes called "multicultural," "diverse," "marginalized," or "under-represented") is often neglected or unknown except by special audiences, or written by marginal or repressed races, classes, or genders.

Popularity or status of representative literature may change in relation to social needs.

Representative literature challenges conventional wisdom and styles from outside.

Representative literature's style may not fit perfectly with dominant-culture styles, but it may challenge or refresh what's become old or "official."

Historic events or references may be unfamiliar to dominant-culture audiences.

However, genres and styles of multicultural outsiders may vary expectations or norms to point of exclusion.

Traditionally-schooled readers may wonder, "What do I do with that?" (The outsider text may challenge ability to read with other texts in schools.)

Representative literature may enjoy some freshness or appeal by being previously unknown or marginalized, eliciting Romantic support for the underdog or outsider.

These categories are not mutually exclusive

Additional notes

Popular literature meets people where they are, confirms their attitudes, values, or self-identifications. It "pushes their buttons."

Formulas and genres are used more or less unconsciously or without embarrassment:

"If this is an action movie, when does the helicopter explode?" (Or, "When does the hero leap through a shattering glass window?")

"If this is a gothic thriller, when's the first scream in the night?" (Or, "When's the first turn-around-and-gasp?")

"If this is a romantic comedy, when does the normative white heterosexual couple meet cute?"

Popular literature throws a lot of contemporary junk into a miscellaneous mix: every page has something that excites or soothes or otherwise interfaces with familiar needs and satisfactions. 

Classic literature often involves "deferred gratification," long attention spans, and unanswered questions or unresolved problems. (Since classic literature doesn't often offer a simple conclusion or wrap-up, the text remains alive in people's minds and continues to challenge future generations.)

Plus classic literature strives for "compositional integrity": parts aren't just thrown together but fit carefully into larger patterns of meaning.

Representative literature:

Religious (or moral) content is sometimes foregrounded, whereas for the dominant culture religion is often repressed, marginalized, or carefully integrated into a secular mix.

Political & historical issues are introduced, often highlighting past injustice and victimization, which complicates "one story" of America's or the world's people.

How is the mix of Classic, Popular, and Representative literature shaking out nationally in terms of what people read in schools?

Classic literature still dominates. Teachers teach what they learned as students.

Possible changes afoot:

Literature > "Humanities," inter-disciplinary study, team-teaching with history, art, etc.

"Read whatever, but read." > reading list becomes what students are capable of reading or willing to read rather than what they should read

Literature courses will probably hang on, more or less.

Example of Popular Literature: film review of Battleship (2012)